oldest earth's rock - acasta gneiss, 4030 ma

4030 acasta amazing ancestral ancient arctic basalt canada canadian continental cratons crust crystals dating eon feldspar geology giga gneiss granite hadean history hornblende longevity metamorphic mica million mineralogy minerals natural northern oceanic oldest plagioclase plate quartz radioactivity rare remote river rock sample science slave specimen tectonics territories weathering years yellowknife zircons